Which is a very good question and makes me wonder about handwashing and restroom services for employees?
When the restaurant has its own restroom you expect to see restaurant employees use it, and that gives you an opportunity to see if they do wash their hands... like the sign says all employees must do.
but when the employees use that "hidden private restroom in the back" you have to wonder, don't you?
You might recall that about a year or so ago I caught floor workers at a major casino in So Cal, including a floor supervisor, who were using the restroom and not washing their hands... in full view of the casino patrons using the same restroom.